Limonene and tetrahydrofurfurly alcohol cleaning agent

ABSTRACT

The present invention is a tetrahydrofurfuryl alcohol and limonene cleaning agent and method for formulating and/or using the cleaning agent. This cleaning agent effectively removes both polar and nonpolar contaminants from various electrical and mechanical parts and is readily used without surfactants, thereby reducing the need for additional cleaning operations. The cleaning agent is warm water rinsable without the use of surfactants. The cleaning agent can be azeotropic, enhancing ease of use in cleaning operations and ease of recycling.

The U.S. Government has rights in this invention pursuant to contractnumber DE-AC04-76-DP00613 with the United States Department of Energy.

This application is a continuation in part of application Ser. No.08/343,651 filed Nov. 22, 1994, now U.S. Pat. No. 5,514,294. Relatedapplication Ser. No. 08/535,897, filed Sep. 28, 1995, also currentlypending, is a divisional application of Ser. No. 08/343,651.

BACKGROUND OF THE INVENTION

Environmental considerations are driving increased use ofenvironmentally-friendly chemicals in manufacturing. Environmentalconsiderations include whether the chemicals are toxic, whether theyhave ozone-depleting properties, whether the chemicals are availablefrom renewable resources, and whether they are biodegradable orrecyclable. Chemical cleaning agents, used in a variety of situationsincluding the manufacture of electrical and mechanical components toremove grease, solder flux, cutting oil and other contaminants from themanufacturing processes, are being examined in light of theseenvironmental considerations. These environmental considerations,coupled with advances in solvent chemistries, have resulted in increaseduse of low-volatility cleaning agents for use with water rinses,commonly referred to as semiaqueous cleaners.

A primary advantage in the use of low-volatility cleaning agents is thereduction in amount of chemicals vaporized as part of the cleaningprocesses. However, because these cleaning agents do not evaporaterapidly, rinses are typically required to remove the cleaning agent fromthe substrate being cleaned.

Some of the semiaqueous cleaners in use involve limonene as a cleaningagent, followed by a water rinse to remove the cleaning agent.(Reference herein to limonene includes the isomers d- and l-limonene andany combination of these isomers.) Because limonene is not miscible inwater, these cleaners require the addition of a surfactant to facilitatewater rinsing. Limonene is specified in various U.S. patents to be usedas a cleaning agent, typically to be blended with surfactants and water.

There are deficiencies in use of limonene as a cleaning agent, however.The surfactants used to allow water rinsing generally are nonvolatilematerials, some of which remain on the substrate being cleaned in areaswhich tend to trap contaminants, such as in joints, in stranded wires,and in nonhermetically sealed assemblies. Further, these limonene andsurfactant cleaning agents generally are not readily distilled becauseof the nonvolatile nature of the surfactants, complicating recycling ofthe cleaning agent for reuse. Finally, limonene is not fully effectivein removing polar contaminants.

Additionally, alcohols are advantageous for cleaning because, typically,they effectively remove polar contaminants. Traditional short-chainlinear alcohols such as isopropyl are flammable and, thus, are difficultto use in automatic cleaning equipment because of the fire and explosionhazards associated with flammable vapors around electrical equipment.The National Electrical Code imposes strict requirements upon equipmentmanufactured to use flammable liquids. Typically, this involves variouscombinations of purging with an inert gas, using explosion-proofelectrical enclosures, or intrinsically safe wiring practices. All ofthese design considerations substantially increase the complexity andcost of utilizing alcohols with low flash points as cleaning agents.Further, alcohols which have traditionally been used as cleaning agentshave relatively high vapor pressure, causing the release of relativelylarge amounts of vapors from cleaning operations.

Long-chain linear alcohols (seven or more carbon atoms) have higherflash points and lower vapor pressures than short-chain alcohols,resolving some of the limitations for using linear alcohols as cleaningagents. However, the long-chain linear alcohols are generally notmiscible in water, and, therefore, require surfactants to allow mixingand rinsing with water. For example, U.S. Pat. No. 5,300,154 discusses,among other things, utilizing long-chain linear alcohols in combinationwith various terpenes, including limonene. These combinations do notappear to be water rinsable without the use of surfactants.

A recent advance in cleaning technologies has been the use ofheterocyclic alcohols, including tetrahydrofurfuryl alcohol.Tetrahydrofurfuryl alcohol is used in biocide and pesticideformulations, paint stripping formulations, fabric dyes, and as acleaning agent. Utilized as a cleaning agent, tetrahydrofurfuryl alcoholtypically is blended with surfactants and water in a cleaning solutionformulated to remove polar contaminants such as solder flux. Althoughthis alcohol is completely miscible in water, the surface tension oftetrahydrofurfuryl alcohol is relatively high (37 dynes/cm) promptingthe use of surfactants to lower the surface tension of the resultingsolution and allow it to more readily wet the substrate being cleaned.Items cleaned with tetrahydrofurfuryl alcohol can be water rinsed andare generally considered organically and inorganically (ionically)clean, although the presence of surfactants presents contaminantproblems similar to those discussed previously.

Ease of recycling of cleaning agents is important to reduce waste andbecause it often is more cost-effective to recycle cleaning agentsrather than to continually replace used cleaning agents with new. Inthis regard, azeotropic or azeotrope-like compositions are desirablebecause they do not fractionate upon boiling. This behavior is desirablebecause azeotropic or azeotrope-like cleaning agents may be distilledfor recycling. In comparison, preferential boiling of the componentswith lower-boiling points of non-azeotrope-like cleaning agents tends toresult in distillate mixtures which have component fractions unlike theoriginal cleaning agents. The changed composition may have lessdesirable or entirely different properties than the original. Therefore,azeotropic and azeotrope-like compositions enhance recycling.

Thus, there is a need for environmentally-friendly, easily recyclable,preferably azeotropic or azeotrope-like, low vapor pressure, high flashpoint cleaning agents which effectively remove both polar and non-polarcontaminants without use of surfactants. The present invention addressesthis need.

DESCRIPTION OF THE INVENTION

The present invention to address the need described above is acomposition which may be used as a cleaning agent, and methods forformulating and using that composition, the composition being comprisedof the components tetrahydrofurfuryl alcohol and limonene in amountseffective to accomplish desired cleaning operations.

The present invention effectively removes both nonpolar contaminantssuch as rosin fluxes, greases, oils, waxes, and tape residues as well aspolar contaminants such as plating salts and flux activators. Indeed, asdisclosed further in the examples below, the cleaning efficacy of thepresent invention unexpectedly far surpasses the individual cleaningcapabilities of either component individually. In addition, the presentinvention has a moderately high flash point and low vapor pressureenhancing its ease and safety of use and environmental friendliness. Forexample, a 50/50 solution by volume of tetrahydrofurfuryl alcohol andlimonene has a vapor pressure of about 2 mm Hg at 20 degrees C (68degrees F.) and a flash point (Pensky-Martens Closed Cup) of about 52.7degrees C. (127 degrees F.). (The low vapor pressure makes accuratevapor pressure measurement difficult, therefore the pressure measurementshown is considered more qualitative than quantitative.) The presentinvention is environmentally-friendly, in that, limonene andtetrahydrofurfuryl alcohol are both made from naturally renewableresources and have no ozone-depletion potential and no known adversehealth effects. Further, a solution of tetrahydrofurfuryl alcohol andlimonene exhibits azeotropic and azeotrope-like properties over a widerange of proportions of the constituents and, thus, is easilyrecyclable. Finally, the composition of the present invention can bewarm water rinsed effectively without surfactants. This combination ofcharacteristics is an unanticipated result of combining these individualcomponents and makes the current invention highly desirable as acleaner, especially in precision cleaning operations.

1. Limonene

The monocyclic terpene, p-mentha-1,8 diene, commonly known as limonene,is a colorless solvent with a high-boiling point. Limonene has theformula: ##STR1## Limonene is commercially available from severalsources including SCM Glidco Organics and Bush Boake Allen, both inJacksonville, Fla. It is manufactured from renewable sources such aspine and citrus products. The flash point of limonene is moderately high(50 degrees C., 122 degrees F.) and the boiling point is high (178degrees C., 352 degrees F.). Refining limonene by distillation canproduce low-odor and high-purity versions. Generally, "commercial grade"limonene contains small amounts (around five percent or less by weight)of other terpene hydrocarbons and may contain a stabilizer such asbutylated hydroxytoluene (BHT). The low-odor, high-purity terpenes havea high solvency for a wide range of non-polar contaminants such asgreases and oils. Terpenes are readily metabolized by bacteria and otherorganisms and rapidly oxidize in the atmosphere, resulting in minimalenvironmental impact. They are classified as Generally Recognized asSafe (GRAS) by the United States Food and Drug Administration and areapproved for human consumption in foods. Terpenes are found in food andfragrance products.

2. Tetrahydrofurfuryl Alcohol

Tetrahydrofurfuryl alcohol, a heterocyclic alcohol, is a colorless, lowodor, pH neutral solvent and has the formula: ##STR2##Tetrahydrofurfuryl alcohol is commercially available from severalsources, including Great Lakes Chemical Corporation, Specialty ChemicalsDivision, in West Lafayette, Ind. and Ashland Chemical Company inColumbus, Ohio. Commercially available or "commercial grade"tetrahydrofurfuryl alcohol typically is 98 percent by weight pure withsmall (under two percent by weight) amounts of furfuryl alcohol and1,5-Pentanediol along with less than one percent by weight moisture anda stabilizer. Tetrahydrofurfuryl alcohol is manufactured from annuallyrenewable agricultural resources and is chemically and thermally stable.As with other heterocyclic alcohols, tetrahydrofurfuryl alcohol's flashpoint (74 degrees C.; 165 degrees F.) is higher and vapor pressure (0.2mm Hg at 20 degrees C., 68 degrees F.) is lower than traditional (shortlinear chain) alcohols, such as isopropyl, methyl, and ethyl alcohol.Heterocyclic alcohols, like traditional alcohols, are miscible in water;tetrahydrofurfuryl alcohol is completely water miscible. Watermiscibility enhances the ability to completely remove a cleaning agentand soils during water rinsing. Tetrahydrofurfuryl alcohol has a highboiling point (178 degrees C.; 352 degrees F.) and a high solvency formost polar contaminants including both organic and inorganic materials.It is nonphotochemically reactive (as defined in California StateRegulations Rule 66) and is an EPA-approved solvent that readilybiodegrades, is completely saturated, and shows low toxicity. It is onlyslightly irritating to the skin and mildly irritating to the eye.

Preferred Embodiment

The composition of the preferred embodiment of the present invention iscomprised of effective amounts of tetrahydrofurfuryl alcohol andlimonene As used herein, "effective amounts" indicates the percentagesof the various components, tetrahydrofurfuryl alcohol and limonene tosatisfactorily clean the item or items to be cleaned. As a practicalmatter, satisfactory cleaning of most polar and non-polar contaminantsis obtained over a wide range of mixtures. However, it may beappropriate in certain circumstances involving primarily polar ornon-polar contaminants to increase the relative percentage of thetetrahydrofurfuryl alcohol component (for polar contaminants) or thelimonene component (for non-polar contaminants). Further, for mostcleaning applications, commercial grades of the components of thecomposition of the present invention provide satisfactory results.

The best test results for the composition of the present invention usedas a cleaning agent have been obtained from a composition composed offrom about 20 to about 80 percent by volume tetrahydrofurfuryl alcoholand from about 80 to about 20 percent by volume limonene and cleaningefficacy appears uniform across that range. The composition may containa stabilizer to inhibit oxidation or polymerization to provide a longershelf life without degradation. Depending upon the particularcontaminant being removed, satisfactory results may be obtained withcomponent fractions outside of the ranges noted.

For example, in situations in which azeotrope-like properties are lessimportant, a range of about 10 to about 90 percent by volumetetrahydrofurfuryl alcohol and about 90 to about 10 percent by volumelimonene may provide acceptable results. Further, in situations where asignificant amount of recycling of the cleaning agent is anticipated,solutions closer to a true azeotropic balance may provide moreacceptable results, such as from about 30 to about 50 percent by volumetetrahydrofurfuryl alcohol and from about 70 to 50 percent by volumelimonene.

The composition of the present invention is formulated by mixingappropriate volumes of the two major components, tetrahydrofurfurylalcohol and limonene, together. If stabilizers are not in the individualcomponents, an appropriate stabilizer may be added to the solution toimprove shelf life if required. As noted in the examples below, thestabilizers typically are removed upon distillation of the solution and,thus, must be re-added to the distillate if required.

In use, the substrate to be cleaned is exposed to the cleaning agent.The method of exposure is dictated by the type of substrate and type ofcontaminant to be removed and includes basically any standard cleaningtechnique including, but not limited to, immersion of the substrate inthe cleaning agent, immersion accompanied by agitation, and spraying thecleaning agent onto the substrate.

The absence of surfactants, along with the use of high purityconstituents, essentially eliminates the amount of nonvolatile residuefrom the cleaning operation. In many cases, satisfactory cleanliness canbe achieved without a final rinse. However, for precision cleaningapplications, it is recommended that a final rinse be performed. Thepreferred rinse is to use high purity deionized water (>10M Ω-cm),heated to at least 40 degrees C. (104 degrees F.). Further, high purityforms of limonene and tetrahydrofurfuryl alcohol are desirable for usein contaminant-sensitive operations. The composition of the presentinvention is formulated to be warm water rinsable without the use ofsurfactants. When exposure to water is undesirable, the composition ofthe present invention can also be effectively rinsed using an alcoholsuch as isopropyl or other traditional alcohols.

As discussed below, the precise azeotropic composition appears to bewithin the range of about 37 to about 39 percent by volumetetrahydrofurfuryl alcohol and from about 63 to about 61 percent byvolume limonene at atmospheric pressure. Regardless of where the trueazeotrope lies, all compositions from about 20 to about 80 percent byvolume tetrahydrofurfuryl alcohol and from about 80 to about 20 percentby volume limonene are azeotrope-like at atmospheric pressure (760millimeters mercury), as defined more particularly below.

The term "azeotrope-like" as used herein is intended to mean that thecomposition behaves like an azeotrope, i.e., has constant-boilingcharacteristics or a tendency not to fractionate upon boiling orevaporation. Thus, in such compositions, the composition of the vaporformed during boiling or evaporation is identical or substantiallyidentical to the original liquid composition. Hence, during boiling orevaporation, the liquid composition, if it changes at all, changes onlyto a minimal or negligible extent. This is contrasted withnon-azeotrope-like compositions in which the liquid composition changessubstantially during boiling or evaporation. As is readily understood bypersons skilled in the art, the boiling point of the azeotrope-likecomposition will vary with the pressure.

It should be noted that the azeotrope-like compositions of the presentinvention may include additional components which do not form newazeotropic or azeotrope-like systems. For example, as noted above, thecomposition of the present invention may contain stabilizers. Typically,however, the stabilizers will be eliminated from the composition in afirst distillation cut taken as described below.

One way to determine whether the addition of a component forms a newazeotropic or azeotrope-like system is to distill a sample thereof underconditions which would be expected to separate the mixture into itsseparate components. If the mixture containing the additional componentis non-azeotropic or non-azeotrope-like, the additional component willfractionate, i.e., separate from the azeotropic or azeotrope-likecomponents. If the mixture is azeotrope-like, some finite amount of afirst distillation cut will be obtained which contains all of themixture components and which is constant-boiling or behaves as a singlesubstance. As used here, the term "first distillation cut" means thefirst cut taken after the distillation column displays steady stateoperation under total reflux conditions.

Because the composition of the present invention is azeotrope-like overa wide range of from about 20 to about 80 percent by volumetetrahydrofurfuryl alcohol and from about 80 to about 20 percentlimonene, it may be recycled by distillation to remove contaminants inthat range or other ranges in which it exhibits azeotrope-likeproperties.

The invention is further illustrated by the following non-limitingexamples:

EXAMPLE 1 & COMPARATIVES

A generally accepted cleanliness test method used in militaryelectronics soldering specifications is an ionic cleanliness test,designated as MIL-P-28809, "Military Specification for Circuit CardAssemblies Rigid, Flexible, and Rigid-Flex." This test measures thechange in resistivity of an isopropyl alcohol and water rinse solutiondue to ionic contamination dissolved and removed from the test sample.In order to verify the effectiveness of the cleaning agent, initialcleanliness testing was performed using a Kenco Industies, Inc. ofAtlanta Georgia Omega Meter Model 600.

Test samples were prepared by depositing a measured amount ofrosin-activated flux on printed wiring assemblies and drag soldering thesamples in a 254-degree C. (490-degree F) solder pot for approximatelyseven seconds. The test samples were then cleaned using a solution of 50percent by volume tetrahydrofurfuryl alcohol and 50 percent by volumelimonene in a 40 kHz ultrasonic cleaning tank for one minute after whichthe samples were blown dry with dry nitrogen. For comparison, other testsamples were cleaned using the above-described procedure withtetrahydrofurfuryl alcohol alone and other test samples were cleanedwith limonene alone.

Laboratory ionic cleanliness testing was conducted on the test samplescleaned. Ionic testing results of the cleaned samples is shown in table1, below.

                  TABLE 1                                                         ______________________________________                                        Ionic Cleanliness, MIL-P-28809                                                                 Ionic Cleanliness,                                                            Average                                                      Cleaning agent   Value (Micrograms NaCl                                       (Percentages are by volume)                                                                    equivalent/Sq. Inch)                                         ______________________________________                                        100 percent limonene                                                                           9.3                                                          100 percent      6.6                                                          tetrahydrofurfuryl alcohol                                                    50 percent limonene and 50                                                                     2.4                                                          percent tetrahydrofurfuryl                                                    alcohol                                                                       ______________________________________                                    

This laboratory testing indicates unexpected synergistic effects ofcombining limonene with tetrahydrofurfuryl alcohol which result in asignificant improvement in cleaning efficacy over either used alone.

The theory for the effectiveness of this cleaning agent for electricalapplications is that the nonpolar limonene component effectively removesthe organic content of the rosin flux contaminant enabling the ioniccontaminants to be removed by the polar component, tetrahydrofurfurylalcohol.

EXAMPLE 2 & COMPARATIVES

More extensive ionic cleanliness testing was performed on sample printedwiring assemblies (PWAs). The PWA test samples were prepared by wavesoldering using a mildly activated rosin flux. The samples were thencleaned in the cleaning agents shown in table 2 using a batch-type spraycleaner for four minutes. Two of the three sample groups were then sprayrinsed for four minutes in 60-degree C. (140-degree F.) deionized water(>1M Ω-cm resistivity) using a batch aqueous cleaner. One set of thelimonene samples also received an isopropyl alcohol (IPA) spray rinsefor one minute and 30 seconds prior to water rinsing. The samples werethen tested in an Alpha Metals, Inc. of Alpharetta, Ga. Omegameter OM700using a 15-minute automatic termination test and an extract solutiontemperature of 41 degrees C. (106 degrees F.). Table 2, below shows thetest data from the ionic cleanliness testing.

                  TABLE 2                                                         ______________________________________                                        Ionic Testing Data                                                                                   Ionic Cleanliness, Average                                                    Value (Micrograms NaCl                                 Cleaning agent                                                                             Rinse     equivalent/Sq. Inch)                                   ______________________________________                                        limonene     IPA       9.5                                                    limonene     IPA spray 6.5                                                                 followed by                                                                   Water                                                            50 percent volume                                                                          Water     2.3                                                    tetrahydrofurfuryl                                                            alcohol & 50                                                                  percent limonene                                                              ______________________________________                                    

This laboratory testing confirms the unexpected synergistic effects ofcombining limonene with tetrahydrofurfuryl alcohol which result in asignificant improvement in cleaning efficacy over limonene used alone.

EXAMPLE 3

Additional testing was performed to assess organic cleaning efficacy ofthe present invention. Test samples were prepared in the same manner asdescribed in the previous ionic cleanliness testing study, example 2above.

A method for measuring organic contamination is the residual rosin test,as described in the Institute for Interconnection and PackagingElectronic Circuits (IPC) document as IPC-TR-580 "Cleaning andCleanliness Test Program Phase 1 Test Results." This test is performedby measuring the change in absorbency of a test sample extract solutionby using an ultraviolet/visible spectrophotometer. The change inabsorbency can then be correlate to micrograms of residual rosin per sq.inch of test sample surface area. In this case, an extract solution of99% IPA and 1% phosphoric acid was used. Each test sample was exposed toan agitated extract solution for one hour prior to solution measurement.Results of the residual rosin testing are shown in table 3, below.

                  TABLE 3                                                         ______________________________________                                        Residual Rosin Testing                                                                                Residual Rosin                                                                (Micrograms Rosin/                                    Cleaning agent                                                                              Rinse     Sq. inch)                                             ______________________________________                                        limonene      IPA       148                                                   limonene      IPA spray 161                                                                 followed by                                                                   Water                                                           50 percent    Water      90                                                   tetrahydrofurfuryl                                                            alcohol & 50                                                                  percent limonene                                                              ______________________________________                                    

Data from the ionic and residual rosin testing demonstrate that thepresent invention is effective as a cleaning agent to remove both thepolar and nonpolar contaminants from rosin flux soldering processes.

EXAMPLE 4

Laboratory analysis was performed on Kovar test samples with gold overnickel plating, some contaminated with Apeizon M vacuum grease, otherscontaminated with Kester 135 rosin flux baked on at 350 degrees C. (688degrees F.) for three minutes. The test samples were then ultrasonicallycleaned at 40 kHz for three minutes with the 1:1 by volumetetrahydrofurfuryl alcohol and limonene cleaning agent and then rinsedwith IPA for one minute. Additional samples were prepared and cleaned asdescribed above with the exception that deionized water was utilized asa rinse in lieu of IPA. Gas Chromatography Mass Spectroscopy (GC/MS) wasperformed on the test samples using a Finnigan-MAT-TSQ-70. Additionaltesting of similarly prepared samples was done using Fourier TransformInfrared Spectroscopy (FTIR) on a Nicolet model 710 with microscopeattachment. Results from both GC/MS and FTIR showed that the Apeizon Mgrease and Kester 135 flux were removed using the cleaning agent andrinses leaving no detectable levels of contamination on the testsamples.

EXAMPLE 5

In order to verify the azeotrope-like nature of the composition of thepresent invention, various solutions of tetrahydrofurfuryl alcohol andlimonene as shown in table 4 were distilled in a Kontes distillationcolumn operated at atmospheric pressure. Comparative analysis of theresulting distillate to the original solutions was performed on a gaschromatograph using a flame ionization detector. The analysis,summarized in table 4, below, indicates that azeotrope-like behaviorappears to exist over a wide range from about 20 to 80 volume percenttetrahydrofurfuryl alcohol with the balance limonene. One notable resultof this testing is that the stabilizers present in the limonene andtetrahydrofurfuryl alcohol were removed in the distillation operation.

                  TABLE 4                                                         ______________________________________                                        Azeotropicity Testing                                                         Solution tested,                                                                            Results                                                         Tetrahydrofurfuryl                                                                          Shift in    Liquid Boiling                                      Alcohol/Limonene,                                                                           Concentration                                                                             Temperature                                         percent volume                                                                              Noted       degrees C.                                          ______________________________________                                        100/0         N/A         178                                                 90/10         Yes         172                                                 80/20         slight      168                                                 70/30         slight      167                                                 60/40         slight      167                                                 50/50         minimal     167                                                 40/60         minimal     167                                                 37/63 to 39/61                                                                              no detectable shift                                                                       166                                                 30/70         minimal     166                                                 20/80         slight      167                                                 10/90         yes         168                                                  0/100        N/A         178                                                 ______________________________________                                    

Based upon this testing, it appears that the solution is azeotropic inthe range of about 37 to 39 percent by volume tetrahydrofurfuryl alcoholwith the balance limonene. Further, the solution is azeotrope-like in abroad band from about 20 to about 80 percent by volumetetrahydrofurfuryl alcohol with the balance limonene.

EXAMPLE 6

In order to verify the ability to utilize the azeotropic characteristicsto distillation-clean the used cleaning agent, solutions of 50 percentby volume tetrahydrofurfuryl alcohol and 50 percent by volume limonene,with a variety of typical contaminants were distilled in a Kontesdistillation column operated at reduced pressure (560 mm Hg).Comparative analysis of the resulting distillate to a standarduncontaminated solution was performed on a GC/MS. The analysis,summarized in table 5, below, indicates that the contaminants wereeffectively removed from the cleaning agent. This indicates that thelimonene and tetrahydrofurfuryl cleaning agent may be recycled forcontinued use, further demonstrating its usefulness and environmentalfriendliness.

                  TABLE 5                                                         ______________________________________                                        Recyclability Testing                                                         Contaminant tested                                                                            Results                                                       ______________________________________                                        No contaminant added.                                                                         .02 percent non-volatile matter in                            GC/MS testing showed                                                                          distillate (distilled once)                                   .12 percent by weight                                                         non-volatile matter                                                           in solution made with                                                         commercial ingredients                                                        .33 percent by weight                                                                         .02 percent by weight contaminant in                          Azepion M vacuum                                                                              distillate (distilled once)                                   grease                                                                        ______________________________________                                    

What is claimed is:
 1. A composition comprised of effective amounts oftetrahydrofurfuryl alcohol and limonene to satisfactorily clean the itemor items to be cleaned, and wherein no surfactant is present.
 2. Acomposition as claimed in claim 1 wherein said tetrahydrofurfurylalcohol and said limonene are commercial grade; wherein commercial gradelimonene contains about five percent or less by weight of other terpenehydrocarbons and may contain a stabilizer such as butylatedhydroxytoluene and wherein commercial grade tetrahydrofurfuryl alcoholis about 98 percent by weight pure with small (under about two percentby weight) amounts of furfuryl alcohol and 1,5-Pentanediol along withless than about one percent by weight moisture and a stabilizer.
 3. Acomposition consisting essentially of effective amounts oftetrahydrofurfuryl alcohol and limonene to satisfactorily clean the itemor items to be cleaned, and wherein no surfactant is present.
 4. Acomposition as claimed in claim 3 wherein said tetrahydrofurfurylalcohol and said limonene are commercial grade; wherein commercial gradelimonene contains about five percent or less by weight of other terpenehydrocarbons and may contain a stabilizer such as butylatedhydroxytoluene and wherein commercial grade tetrahydrofurfuryl alcoholis about 98 percent by weight pure with small (under about two percentby weight) amounts of furfuryl alcohol and 1, 5-Pentanediol along withless than about one percent by weight moisture and a stabilizer.
 5. Acomposition, comprising from about 10 to about 90 percent by volumetetrahydrofurfuryl alcohol and from about 90 to about 10 percent byvolume of limonene, and wherein no surfactant is present.
 6. A method offormulating a composition consisting essentially of the step of mixingfrom about 10 to about 90 percent by volume tetrahydrofurfuryl alcoholwith from about 90 to about 10 percent by volume of limonene, andwherein no surfactant is present.
 7. A composition as claimed in claim5, wherein the concentration percent by volume of saidtetrahydrofurfuryl alcohol is from about 30 to about 50 and theconcentration percent by volume of said limonene is from about 70 toabout 50, and wherein no surfactant is present.
 8. A method offormulating a composition as claimed in claim 6 wherein the percent byvolume of said tetrahydrofurfuryl alcohol is from about 20 to about 80and the percent by volume of said limonene is from about 80 to
 20. 9. Anazeotrope-like composition, consisting essentially of from about 20 toabout 80 percent by volume tetrahydrofurfuryl alcohol and from about 80to about 20 percent by volume limonene which composition boils at about166 degrees centigrade at a pressure of about 760 millimeters mercury,and wherein no surfactant is present.
 10. An azeotrope-like compositionas claimed in claim 9 wherein the concentration percent by volume ofsaid tetrahydrofurfuryl alcohol is from about 30 to about 50 and theconcentration percent by volume of said limonene is from about 70 toabout
 50. 11. An azeotrope-like composition as claimed in claim 9wherein the concentration percent by volume of said tetrahydrofurfurylalcohol is from about 37 to about 39 and the concentration percent byvolume of said limonene is from about 63 to about
 61. 12. A method offormulating a composition comprising the step of mixing from about 10 toabout 90 percent by volume tetrahydrofurfuryl alcohol with from about 90to about 10 percent by volume of limonene, and wherein no surfactant isadded.
 13. A method of formulating a composition as claimed in claim 12wherein the percent by volume of said tetrahydrofurfuryl alcohol is fromabout 20 to about 80 and the percent by volume of said limonene is fromabout 80 to
 20. 14. A method of formulating a composition as claimed inclaim 12 wherein the percent by volume of said tetrahydrofurfurylalcohol is from about 30 to about 50 and the percent by volume of saidlimonene is from about 70 to
 50. 15. A method of formulating acomposition as claimed in claim 12 wherein the percent by volume of saidtetrahydrofurfuryl alcohol is from about 37 to about 39 and theconcentration percent by volume of said limonene is from about 63 toabout
 61. 16. A method of formulating a composition as claimed in claim6 wherein the percent by volume of said tetrahydrofurfuryl alcohol isfrom about 30 to about 50 and the percent by volume of said limonene isfrom about 70 to
 50. 17. A method of formulating a composition asclaimed in claim 6 wherein the percent by volume of saidtetrahydrofurfuryl alcohol is from about 37 to about 39 and theconcentration percent by volume of said limonene is from about 63 toabout 61.